一番使い勝手の良いemacsのcompanyモードの設定を紹介

(use-package company
  :ensure t
  :after company-statistics
  :bind (("M-<tab>" . company-complete) ;; Tabで自動補完を起動する
         :map company-active-map
         ;; C-n, C-pで補完候補を次/前の候補を選択
         ("M-n" . nil)                      ;; M-nで次の候補への移動をキャンセル
         ("M-p" . nil)                      ;; M-pでの前の候補への移動をキャンセル
         ("C-n" . company-select-next)      ;; 次の補完候補を選択
         ("C-p" . company-select-previous);; 前の補完候補を選択
         ("C-s" . company-filter-candidates) ;; C-sで絞り込む
         :map company-search-map
         ;; 検索候補の移動をC-nとC-pで移動する
         ("C-n" . company-select-next)
         ("C-p" . company-select-previous))
  :init
  ;; 全バッファで有効にする
  (global-company-mode)
  :config
  (define-key emacs-lisp-mode-map (kbd "C-M-i") nil) ;; CUI版のためにemacs-lisp-modeでバインドされるC-M-iをアンバインド
  (global-set-key (kbd "C-M-i") 'company-complete)   ;; CUI版ではM-<tab>はC-M-iに変換されるのでそれを利用
  (setq completion-ignore-case t)
  (setq company-idle-delay 0)                    ;; 待ち時間を0秒にする
  (setq company-minimum-prefix-length 2)         ;; 補完できそうな文字が2文字以上入力されたら候補を表示
  (setq company-selection-wrap-around t)         ;; 候補の一番下でさらに下に行こうとすると一番上に戻る
  (setq company-transformers '(company-sort-by-occurrence company-sort-by-backend-importance))) ;; 利用頻度が高いものを候補の上に表示する

(use-package company-statistics
  :ensure t
  :init
  (company-statistics-mode))

;; auto-completeに近い挙動で候補の絞り込みができる
(use-package company-dwim
  :straight '(company-dwim
              :type git
              :host github
              :repo "zk-phi/company-dwim")
  :ensure t
  :init
  (define-key company-active-map (kbd "TAB") 'company-dwim)
  (setq company-frontends
      '(company-pseudo-tooltip-unless-just-one-frontend
        company-dwim-frontend
        company-echo-metadata-frontend)))

;; カーソルの位置がどこであってもcompanyを起動できる
(use-package company-anywhere
  :straight '(company-anywhere
              :type git
              :host github
              :repo "zk-phi/company-anywhere")
  :ensure t)

;; プログラムの関数、変数のキーワード補完を強化
(use-package company-same-mode-buffers
  :straight '(company-same-mode-buffers
              :type git
              :host github
              :repo "zk-phi/company-same-mode-buffers")
  :after company
  :ensure t
  :init
  (require 'company-same-mode-buffers)
  (company-same-mode-buffers-initialize)
  ;;
  :config
  (setq company-backends
        '((company-capf :with company-same-mode-buffers)
          (company-dabbrev-code :with company-same-mode-buffers)
          company-keywords
          company-files
          company-dabbrev)))

(defun show-file-name ()
  "Show the full path file name in the minibuffer."
  (interactive)
  (message (buffer-file-name)))
(defun show-file-name2 ()
  "Show the full path file name in the minibuffer."
  (interactive)
  (message (buffer-file-name)))
(defun show-file-name3 ()
  "Show the full path file name in the minibuffer."
  (interactive)
  (message (buffer-file-name)))

(company-bbdb
 company-semantic
 company-cmake
 company-capf
 company-clang
 company-files
 (company-dabbrev-code company-gtags company-etags company-keywords)
 company-oddmuse
 company-dabbrev)

  (setq company-backends
        '((company-capf :with company-same-mode-buffers)
          (company-dabbrev-code :with company-same-mode-buffers)
          company-keywords
          company-files
          company-dabbrev)))